1. Field of the Invention
The present invention relates to a hydraulic retarder compact in size and capable of reducing the number of rotating parts provided between an operation fluid filled within a casing of the retarder and atmosphere outside the casing.
2. Related Art
There has been known a conventional hydraulic retarder for large-sized vehicles such as buses, trucks, etc. The conventional hydraulic retarder of this type produces a braking torque when, for example, the vehicle goes down a sloping road or the vehicle running at high speed is to decelerate abruptly, to thereby suppress an undesired fade phenomenon and, therefore, improve a safety and durability of friction materials of the bake.
One example of the conventional hydraulic retarder is as disclosed in commonly assigned U.S. Pat. No. 4,828,079. According to the hydraulic retarder described in this patent, a clutch apparatus is disposed outside a casing of the hydraulic retarder and a cylinder apparatus for driving the clutch apparatus to engage/disengage is also disposed outside the casing. The hydraulic retarder of this type is provided with rotatable rotor vanes secured to a rotating shaft such as a propeller shaft rotating with vehicle wheels, and unrotatable stator vanes secured to a vehicle body. When the rotor vanes are engaged with the rotational shaft by an operation of the clutch apparatus, the retarder produces a braking torque by a speed energy of an operation fluid flowing between the stator vanes and rotor vanes. The operation fluid is always filled within the retarder casing accommodating therein the stator vanes and rotor vanes.
The conventional hydraulic retarder as described above saves internal space of the casing for accommodating the vanes since the clutch apparatus is disposed outside the casing. However, the cooling effect of the operation fluid is not applied to the clutch apparatus. Further, the hydraulic retarder of this type may readily suffer from a problem in occurring a leakage of the operation fluid because the retarder has many rotating or sliding parts or portions connecting between the operation fluid filled within the casing and atmosphere outside the casing.